1. Field of the Invention
The invention relates to an anti-jackknifing method and apparatus, and particularly to such an apparatus and method for a tow vehicle-trailer arrangement.
2. Description of the Prior Art
A tow vehicle-trailer arrangement in which the trailer is articulated or capable of lateral movement independently of the tow vehicle is subject to sideways skidding of jackknifing of the trailer out of control of the driver. This dangerous condition frequently occurs when the tow vehicle or truck and trailer are heavy-duty vehicles operating in an empty or lightly loaded condition on wet or slippery roads. Braking by the driver must be carefully controlled to prevent the trailer from skidding laterally or jackknifing.
Federal and State authorities have required that heavy-duty truck-trailer combinations be equipped with electronic anti-skid systems or the equivalent to provide automatic maintenance of brake balance. It is believed that the skid control systems developed to satisfy such requirements all operate on the principle that brake unbalance is the primary cause of truck jackknifing accidents.
A typical prior art system becomes operative whenever the angular relationship between the tow vehicle and the trailer undergoes a predetermined change. The system sends separate braking commands to the various brakes to compensate left and right braking forces to thereby maintain stability. U.S. Pat. No. 3,894,773, issued July 15, 1975, and entitled "Differential Braking System for Tractor-Trailer Trucks", discloses one such system.
U.S. Pat. No. 3,993,362, issued Nov. 23, 1976, and entitled "Anti-Jackknifing and Skidding Control System", teaches a system utilizing a linear accelerometer located on the rear of the trailer to detect left or right skidding and to provide automatic differential braking to the left or right wheels, depending upon the direction of skidding.
Such prior art systems are relatively expensive, sophisticated, and usurp braking control of the tow vehicle and trailer from the driver. In addition, certain automatic skid control systems of the prior art have malfunctioned to such an extent that truck operators are hesitant to rely upon them.
In summary, the systems of the prior art do not provide a simple and inexpensive way of enabling a tow vehicle-trailer combination to be effectively braked and at the same time keep the trailer from jackknifing.